Appendix II 787 lastly the pattern is withdrawn upward or the box downward. Woolnough and Dehne's machine, Fig. 765, provides for a raising of the pattern, a turning over, and removal of box on a short tramway. R R are the rails, clamped at a convenient height, x a table on wheels, P a pattern plate, turning over when required, and at other times clamped horizontally by screws A A. The pattern halves x: and v are first screwed to this plate in mutual correspondence, and the raising and lowering is performed by levers M M, which act on pinions Q Q through shaft s, thereby moving racks K K. The upper ends of the racks support sleeves L L, which carry trunnions N NT, thus lifted or depressed as required. The operations can now be understood. Assuming the box on the top of the plate as at a} it is filled with sand and rammed, the screws A. A and the cotter bolts preventing rotation and lifting respectively, These screws are next released, the plate raised, and the box turned through 180° into position £, an intermediate raising being necessary, Lastly, the cotters are withdrawn, the plate raised, and the box removed by the tramway. This leaves the x half of pattern uppermost, and the previous operations being repeated for it also, the boxes are bolted together for casting. To avoid the lost time due to raising and turning over, Mr. J. Maclellan has devised a machine where P is rigid, and the box, being always right side up, is filled with sand and lifted till it meets the pattern. The ramming is then performed hydraulically, by the raising of a second box of sand, which is pressed against the first one, thus squeezing some of its contents through the ribs and producing the necessary consistency. (Ste p. 969.) P, 42. Whitworth Compressed Steel.—Seep. 790. CHAPTER II. P. 44. "Woods.—Passing inward through a tree section, one meets in order the bark, sapwood, heartwood, and pith. Trie heartwood is best, and the sapwood should be ayoided if possible.